The production of hydrogen and carbon monoxide has traditionally been performed by reforming hydrocarbons such as methane in the presence of steam and a catalyst. Reforming of hydrocarbons typically results in a synthesis gas which may contain hydrogen, carbon monoxide, carbon dioxide, steam and methane. Hydrocarbon reforming is an endothermic process which requires significant heat input to affect reaction. Typically in providing sufficient heat to drive the endothermical hydrocarbon reformation reaction, significant heat losses are accommodated by the production of excess steam. In many instances, excess steam is not usable or desired. In addition, an array of heat exchange equipment is necessary to recover all of the high temperature useable heat created to drive the endothermic hydrocarbon reformation reaction. Conventional reformers in general have two separate heat exchange trains which are composed of a series of two-stream discrete heat exchange units. The first train cools the reformer furnace flue gas to a low temperature against reformer steam/hydrocarbon feed, vaporizing and possibly super-heating steam, condensate heating and hydrocarbon heating. This heat exchange is generally carried out in adducted heat exchange unit, in which the heating streams exchange heat with the flue gas in discrete tube banks of plain or finned tubes. The second train cools the high pressure reformed gases from the reformer furnace in a waste heat boiler followed by a series of separate shell and tube, two-fluid heat exchangers against preheating feed gas streams, process condensate, etc. A large part of the cost of a reformer lies in these two heat exchange systems with their associated piping. Attempts have been made to produce simpler, more cost effective heat transfer systems. The reformer can be designed to include convection heat transfer so that the hot reformed gas is used to preheat feed or provide part of the heat for the reforming reaction. Some heat exchange units use a separate hot gas heat exchanger and some have concentric tubes in the reformer furnace with catalyst in the annulus and product gas flowing through the inner tube, thus the reacting gas mixture is heated from the furnace side and from the inside simultaneously. Reformers of this type have lower product gas exit temperatures than conventional reformers, giving reduced size waste heat boilers and are capable of operating efficiently with little or no export steam production. Attempts have been made to provide more effective heat integration in reforming reactions, but such attempts have not succeeded in combining the identified two separate heat exchange trains into a single heat exchange function.
Heat exchangers which used an annular space to heat exchange flue gas and reformate against steam and hydrocarbon to be reformed are typified by U.S. Pat. No. 4,071,330 which shows such an apparatus. This patent does not show additional heat exchange function to preheat feed, cool reformate or extract additional heat from flue gas.
Shell and tube heat exchange function as described above is exemplified by U.S. Pat. Nos. 3,971,847 and 3,982,910. These patents utilize shell and tube heat exchange apparatus to preheat hydrocarbons and air prior to partial oxidation reformation to produce hydrogen rich product. These processes are limited in the number of streams which can be heat exchanged one against the other due to the shell and tube construction wherein one gas stream must occupy the entire shell region while another gas stream occupies the tube region.
U.S. Pat. No. 3,992,168 discloses a plate-type heat exchanger that is used to rectify the components of a mixed gas stream, such as the recovery of hydrogen from a mixture such as "purse" gas in an ammonia synthesis gas, off-gas purification of petroleum or coke oven gas. Such a rectifying plate heat exchanger operates in the context of a dephlegmator.
Other plate type heat exchangers and plate-fin type heat exchangers are disclosed generically in U.S. Pat. Nos. 4,858,685; 4,890,670 and 5,035,284. These plate type heat exchangers are not identified for any particular service or process duty.
U K. Patent Application GP2066841 discloses a saturation system for saturating a reformer feed with water prior to heating the saturated reformer feed in the flue gas of a traditional reformer which reforms the reforming feed as a feed gas to a methanol reactor.
U.S. Pat. No. 4,681,603 discloses a process for direct injection of water into a reformer feed in a coil-wound heat exchanger heated by reformer flue gas or shift reactor effluent. The saturated reformer feed is then passed through a separator to remove excess condensate and sent to a reformer to reform the feed to appropriate product slate.
The present invention overcomes the drawbacks of the prior art of using a plurality of separate heat exchangers and, with regard to some prior art, of the production of excess steam for energy efficiency, by the utilization of a unique multistream compact heat exchange function, as will be more clearly described below.